Novel Ribonuclease Activity Differs between Fibrillarins from Arabidopsis thaliana

Abstract

Fibrillarin is one of the most important nucleolar proteins that have been shown as essential for life. Fibrillarin localizes primarily at the periphery between fibrillar center and dense fibrillar component as well as in Cajal bodies. In most plants there are at least two different genes for fibrillarin. In Arabidopsis thaliana both genes show high level of expression in transcriptionally active cells. Here, we focus on two important differences between A. thaliana fibrillarins. First and most relevant is the enzymatic activity by AtFib2. The AtFib2 shows a novel ribonuclease activity that is not seen with AtFib1. Second is a difference in the ability to interact with phosphoinositides and phosphatidic acid between both proteins. We also show that the novel ribonuclease activity as well as the phospholipid binding region of fibrillarin is confine to the GAR domain. The ribonuclease activity of fibrillarin reveals in this study represents a new role for this protein in rRNA processing.

Ribosome Biogenesis in Plants: From Functional 45S Ribosomal DNA Organization to Ribosome Assembly Factors

“…Indeed, FIBRILLARIN methylates histone H2A on rRNA gene promoters in both humans and Brassica species (Tessarz et al, 2014;Loza-Muller et al, 2015). Furthermore, a ribonuclease activity was demonstrated for the GAR domain of Arabidopsis FIB2 but not for that of FIB1 (Rodriguez-Corona et al, 2017). Because FI-BRILLARIN copurifies with the NUCLEOLIN-U3 snoRNP complex, it was suggested that FIB2 might be involved in the cleavage of the P site in the 59ETS (Rodriguez-Corona et al, 2017).…”

“…Furthermore, a ribonuclease activity was demonstrated for the GAR domain of Arabidopsis FIB2 but not for that of FIB1 (Rodriguez-Corona et al, 2017). Because FI-BRILLARIN copurifies with the NUCLEOLIN-U3 snoRNP complex, it was suggested that FIB2 might be involved in the cleavage of the P site in the 59ETS (Rodriguez-Corona et al, 2017). More recently, analysis of fib2 knockout plants demonstrated that FIB2 binds to and negatively regulates the expression of innate immune response genes in Arabidopsis.…”

Fibrillarin evolution through the Tree of Life: Comparative genomics and microsynteny network analyses provide new insights into the evolutionary history of Fibrillarin

“…For these searches, considering that fibrillarin is highly conserved across lineages (from Archaea to Eukarya [ 1 , 2 ]), the queries were the human FIB protein (NP_001427.2) and the AtFIB2 protein from A . thaliana (NP_567724.1), as these proteins are functionally well characterized [ 94 – 96 ]. We use this model to detect fibrillarin sequences on the 1049 selected genomes across the three domains of life.…”

“…We built a Hidden Markov Model (HMM) from the fibrillarin domain (Pfam: PF01269) of 450 unique fibrillarin sequences retrieved from a psi-blast analysis (3-iterations in each search; [93]) against the nr database from the NCBI and the refseq-protein databases from Fungi (taxid:4751), Alveolata (taxid:33630), Rhizaria (taxid:543769), Amoebozoa (taxid:554915), Bacteria (taxid:2), and Archaea (taxid:2157). For these searches, considering that fibrillarin is highly conserved across lineages (from Archaea to Eukarya [1,2]), the queries were the human FIB protein (NP_001427.2) and the AtFIB2 protein from A. thaliana (NP_567724.1), as these proteins are functionally well characterized [94][95][96]. We use this model to detect fibrillarin sequences on the 1049 selected genomes across the three domains of life.…”

https://researchopenworld.com/stress-and-cell-death-in-brassica/#

“…One way of p53 to inhibit tumor formation is by the negative transcriptional regulation of fibrillarin (fib), a nucleolar protein with metyltransferase activity, which processes ribosomal RNA (rRNA) maturation and assemble of ribosomes [48,[55][56][57][58] , and has been related with virus movement and systemic infection in plants [59,60]. Partial silencing of p53 in immortalized human mammary epithelial cells (HME) produces overexpression of fib, leading to changes in the methylation of rRNA that results in changes of translation fidelity, showed by the bypass of added stop codon addition in rRNA and amino acid miss incorporation and alter translation initiation [53].…”